Power conversion system

Abstract

A power conversion system comprises a plurality of power modules, each including a power input end; a charging input end; a power output end; at least one power conversion unit, each including an AC / DC conversion unit and at least one DC-Bus capacitor and being connected to the power input end and the power output end; and a pre-charging unit connected to the charging input end for receiving direct current and connected to the DC-Bus capacitor. The pre-charging unit starts to charge the DC-Bus capacitor of one of the power modules when said power module breaks down or the load of the power conversion system is light so that no current flows through the AC / DC conversion unit. The power input ends of the power modules are connected in series and then connected to an AC power source, and the power output ends of the power modules are connected in parallel.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS[0001]This non-provisional application is a Continuation-In-Part application of patent application Ser. No. 16 / 423,147 filed in the U.S. on May 27, 2019 which claims priority to China Application Serial Number 201810708851.X, filed Jul. 2, 2018, the entire contents of which are hereby incorporated by reference.[0002]Some references, if any, which may include patents, patent applications, and various publications, may be cited and discussed in the description of this invention. The citation and / or discussion of such references, if any, is provided merely to clarify the description of the present invention and is not an admission that any such reference is “Prior Art” to the present invention described herein. All references listed, cited, and / or discussed in this specification are incorporated herein by reference in their entireties and to the same extent as if each reference was individually incorporated by reference.BACKGROUND OF THE PRESENT I...

AI Technical Summary

Benefits of technology

The invention provides a system to efficiently pre-charge the capacitors in power modules, which can make the pre-charging circuit smaller and more power-efficient.

Problems solved by technology

However, the pre-charging of DC-Bus capacitors in the combination-typed power converter becomes a new bottleneck.

1) First, it is limited to the voltage levels of the main power circuits in the power modules 1 to N. The soft-start resistors RA, RB, and RC, and the switches SA, SB, and SC are required to be medium-voltage elements, which are large in size and lead to a high cost. For example, the size of a 10 kV SVG pre-charging circuit may be 600 mm*600 mm*600 mm in volume. Further, in control of those switches SA, SB, and SC, the voltage level isolation at medium voltage has to be taken into consideration.

2) Second, since the pre-charging circuit is disposed in the main power circuit, the pre-charging circuit can only be fed with medium-voltage alternating current passively. The power modules 1 to N cannot be hot-plugged.

3) Third, since the soft-start resistors RA, RB, RC are connected in series to a main power circuit between respective power input ends of the power modules 1 to N and respective medium voltage inputs of the system, the entire system may not work when the soft-start resistors RA, RB, RC or the switches SA, SB, and SC fails.

4) Fourth, the pre-charging can only be done at one time. If additional control is not provided, there may be a risk of unbalance in capacitor voltage.

5) Fifth, when grid voltage changes, the soft-start resistors RA, RB, RC, and the switches SA, SB, SC have to be redesigned.

1) First, since the soft-start resistors and the switches in the pre-charging circuit are connected in series to the main power circuits of the power modules 1 to N, the current levels of those soft-start resistors and switches have to be selected depending on the current levels of the main power circuits of each power module. Therefore, those soft-start resistors and switches have a large volume. For example, the size of a single switch is not less than 50.5 mm*32.9 mm*36 mm in volume. Further, too many switches may increase the cost of the system.

2) Second, since the soft-start resistors and the switches in the pre-charging circuit are connected in series to the main power circuit of the power modules 1 to N, the entire system may not work when some soft-start resistor or some switch fails.

3) Third, since the pre-charging circuit is disposed in the main power circuit, the pre-charging circuit can only be fed with medium-voltage alternating current passively.

4) Fourth, the pre-charging can only be done at one time. If additional control is not provided, there may be a risk of unbalance in capacitor voltage.

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